The major objectives of this research are: Clinical Studies. To continue the study of uninterrupted pacing of the diaphragm conditioned to resist fatigue in patients with respiratory paralysis. To carry out a detailed review of the present status and past course of patients with central alveolar hypoventilation (CAH) treated by diaphragm pacing (DP) at the Yale-New Haven Medical Center in an effort to identify those factors that affect the prognosis of this type of patient. Particular emphasis will be on studies concerning: 1) the neurologic manifestations; 2) the ventilatory response to "normocapnic" hypoxia, hypercapnic hyperoxia and hypercapnic hypoxia prior to the instituting of diaphragm pacing and afterwards; 3) the electrical parameters used at the start of pacing and subsequently; 4) the movement of the diaphragm on and off diaphragm pacing; 5) the occurrence of upper airway obstruction on and off diaphragm pacing; 6) the pulmonary function, including ventilation and perfusion lung scans, prior to the institution of pacing and afterwards; 7) the causes for and the frequency of the need to pace both hemidiaphragms in patients with CAH; 8) the respiratory complications that appear to be related to or influenced by the pacing technique; 9) the transdiaphragmatic pressure (Pdi); and 10) the conditioning of the diaphragm using the accelerometer technique during pacing. To update the national (and international) registry on diaphragm pacing. Experimental Studies. To evaluate to totally implantable phrenic nerve stimulator and programmer of a new design (pulse width modulated). To explore the optimum pulse frequency and pulse train repetition rate for intermittent pacing of the diaphragm, a) for ventilatory support, b) for controlling the diaphragmatic component of singultus.